A customer enters the identification associated with one of the many viewable products within a glass front vendor and makes a two digit entry on a keypad or selection buttons located away from the viewed products. Many different selection methods are used to select products from a vending machine, ranging from depressing alpha-numeric marked buttons that activate sensors, to the touching of identified areas on a screen or panel.
Many known technologies for identifying areas of touch on a screen could be utilized such as Acoustic Pulse Recognition (APR) which comprises a glass display overlay or other rigid substrate, with four piezoelectric transducers mounted on the back surface. The transducers are mounted on two diagonally opposite corners out of the visible area and connected via a flex cable to a controller card. The impact when the screen is touched, or the friction caused while dragging between a user's finger or stylus and the glass, creates an acoustic wave. The wave radiates away from the touch point, making its way to the transducers which produce electrical signals proportional to the acoustic waves. These signals are amplified in the controller card and then converted into a digital stream of data. The touch location is determined by comparing the data to a profile. The APR is designed reject ambient and extraneous sounds, as these do not match a stored sound profile. The key is that a touch at each position on the glass generates a unique sound. Four tiny transducers attached to the edges of the touch-screen glass pick up the sound of the touch. The sound is then digitized by the controller and compared to a list of prerecorded sounds for every position on the glass. The cursor position is instantly updated to the touch location. By using the sound generated when a finger or stylus touches the glass, APR allows users to touch the screen with practically anything, such as a fingernail, gloved hand, pen or corner of credit card.
Dispersive Signal Technology (DST) represents a fundamentally different approach to touch. Unlike other solutions that recognize touch by the interruption of electrical fields, acoustic waves, optical fields, or infrared light, Dispersive Signal Technology recognizes touch by interpreting bending waves created in the overlay substrate via the impact of a touch. DST locates sensors in each corner of the touch screen, which measure the vibration energy. Advanced dispersion adjustment algorithms are then applied to the data, allowing accurate reporting of each touch. This approach helps eliminate issues with screen contaminants and surface scratches, and also allows a touch to be registered while a palm and/or object is resting on the screen's surface. A finger, gloved hand or stylus can initiate a touch while a person's palm and drink are on the surface. The touch creates a vibration, which radiates a bending wave through the substrate from the point of contact spreading out to the edges, and the resting items are ignored as they do not generate any vibration energy.
An established technology using waves to detect contact is Surface Acoustic Wave (SAW), which generates high frequency waves on the surface of a glass screen, and their attenuation by the contact of a finger, is used to detect the touch location. This technique is “time-of-flight”, where the time for the disturbance to reach one or more sensors is used to detect the location. Such an approach is possible when the medium behaves in a non=dispersive manner i.e. the velocity of the waves does not vary significantly over the frequency range of interest. A contact sensitive device comprising a member capable of supporting bending waves, having a plurality (e.g. three or more) sensors mounted on the member for measuring bending wave vibration in the member, whereby each sensor determines a measured bending wave signal. A processor calculates a location of a contact on the member from the measured bending wave signals, in that the processor calculates a phase angle for each measured bending wave signal, and then calculates a phase difference between the phase angles of least two pairs of sensors from which the location of the contact is determined. Ultrasonic acoustic wave contact detecting apparatuses are in widespread use. Examples of their applications include operating screens of personal computers, ticket dispensers at train stations, copiers installed in convenience stores and ATM's at financial institutions. These acoustic wave contact detecting apparatus utilize transducers, including piezoelectric vibrators provided on a substrate (touch panel) formed of glass or the like. These transducers function both as generating means for bulk waves and as sensors for detecting acoustic waves which are scattered by a finger or the like that contacts the touch panel. The surface acoustic waves are scattered by a finger or the like. The scattering of the surface acoustic waves is detected by detection means. The detected signal is referenced against a clock signal of a controller, and the position at which the surface acoustic waves are scattered is determined.
Another method for locating the positions of fingers knocking on a pane of glass is Acoustic Tap Tracking (ATT). The finger tap excitation can change considerably from one hit to the next. Variations occur depending on how the glass is struck, the type of glass used, and how the glass is supported. Contact pickups made of polyvinylidene fluoride (PVDF) piezoelectric foil 52, are placed near the perimeter of a glass pane produce signals when the glass is hit. They are bonded with common adhesive to a glass window solidly supported by rubber anchors along its entire perimeter. To track taps more reliably, using a simple static threshold is generally not adequate. Amplitude dependence is one factor, because the leading edge for a knuckle-tap is not sufficiently abrupt. The characteristics of the first arrival can vary widely from transducer to transducer and impact to impact. A significant problem posed by the variable amount of low-amplitude, higher-frequency, dispersive deflection often arrives before the main wavefront. Likewise, sharp impacts (e.g., snapping a metal ring against the glass instead of one's knuckle) excite rapidly moving modes. A microcontroller continuously digitizes the analog signals, from four transducers into 10 bits at over 10 kHz enables a more detailed and robust embedded analysis to look at other waveform features (e.g., peak amplitudes and waveform shape) for each tap. The microcontroller continuously samples the signals from each transducer into a rotating buffer. Upon detecting a transducer signal above a noise threshold, a “knock” event is declared, and 10 millisecond (ms) worth of data are stored from all four inputs (including 3 ms of data before the trigger occurs). This buffer is then scanned for every significant peak in the absolute-value waveform produced by each transducer, and descriptive parameters (e.g., peak height, width, and mean arrival time relative to the initial trigger) are extracted for each peak including any small peaks arriving earlier. These parameters are sent, together with a count of the number of zero-crossings across the data acquisition interval (too many zero crossings indicate a sharp hit with different timing). A connected personal computer then processes the timing determined for each first peak by a second order polynomial that was obtained from a linear least-squares fit to a set of calibration to produce an estimate of the impact location in Cartesian coordinates. In addition to increasing the reliability of the results, the use of a microcontroller readily enables more channels of gestural input (e.g., measuring the strike intensity and classifying the type of strike). Also extracted is an estimate of accuracy or validity by crosschecking the detected waveform characteristics from the different sensors and examining the differences between the four position estimates obtained from the four different sensor triplets (since there are four pickups, there is one redundant degree of freedom). The sensor strips are very small and do not significantly block the window's view.
The present invention provides a simple method to utilize the typical double glass pane construction of a refrigerated glass front vending machine for making product selections on the glass front without modifying the glass panes or their support, and without requiring sensors on the outer glass pane. It does not require the generation of high frequency waves, nor does it utilize the high frequency sounds from the touching of the outer glass pane.